ASP CLassic Mode? What is it and will it effect error pages?

Hello, today I noticed my error pages were not working on my server..
They have been working for the last 4 months...

Does ASP classic mode have anything to do with this  and should I be running in  Asp classic mode.  
My site is new and I don't think I should need classic mode. I am just running ASP includes

Does anyone know what could be the common cause for error pages to stop working.

Hope this is not a two part question, I alreade broke it up into two.

The other is here.
https://www.experts-exchange.com/questions/24565484/Web-Config-File-in-IIS7-Windows-2008-Needs-A-look-at.html

Windows Server 2008
Pentium Dual Core
6GB DDR2 Ram
Power Button
Mouse
...........LOL



Thank you in advance
Selvol